This isn't just some random targetWhy expend so much effort? Sure, your original prey decided to hole up in someone's house. Why not move on to the next house? Or the next guy wandering the streets? Unless, of course, this isn't just a random bystander. Two likely scenarios:
America is a one-party stateFrom going on their website  one can see there is no reference to any political party other than the one promoted all over the pages: the New Founders of America, NFA. There is, though, reference to unity, and strength through Purging. The corruption, stagnation, and decay of multi-partisan democratic government is passive-aggressively denounced, and there are hints of a mass political reorganization under the NFA, which they refer to as the "Great Integration". This means America as we know it is dead, though they still use the familiar symbols of American democracy, such as the same federal government, the state governments, the Statue of Liberty, the Constitution, etc. America has traded freedom for safety, forgetting Benjamin Franklin's words, and making a mockery of the original America. The Party symbol is revered as almost a new national symbol: the blue baptisia flower.
The guy who wanted to kill his boss ended up getting killed by said boss.
The leaders of this society have a deal with the elder gods, sort of like The Cabin in the Woods, except on a more massive scale.In return for a massive human sacrifice on Purge night they get prosperity for the rest of the year.
One of the members of the New Founding Fathers is Princess MorebucksC'mon! She started The Purge in Townsville before!
The Purge is a pseudo-sequel to The Running Man
There are a whole lot of 5-and-under children with birthdays in December.
The first Purge or two weren't murder sprees.For every American who wanted to get their kill on, there must have been 5-10 who heard "nothing is forbidden, everything is permitted" and thought "gee, I've always wanted to smoke some dope/hire two hookers/drive 90 mph on the highway" or other similar crimes. That first night, plenty of people were out doing a wide cross-section of petty crimes and misdemeanors. But the next year, when the bona-fide whackos are sure that the Purge isn't just some trick to get people to incriminate themselves, the blood starts to really flow, with the petty offenders providing a target-rich enviroment for your spree killers and oppourtunity rapists. The 364 days after that are when people really start preparing for a lockdown, leading to the situation as of the film's Purge.
The series will be subject to constant Genre Shift.The first film was Home Invasion, the creators have said the second film will be about people out on the streets trying to survive. At some point, though, we have to start going political thriller, to try to find out more about the Bigger Bad the New Founding Fathers, and after that we'll get a rebellion that will basically create a war movie.
The sequels will eventually see the duration of the Purge extended.Likely as part of an anniversary event (the founding of the New America) or as a means of quelling a coming revolution. It will be extended from 12 hours to a day, a week or even longer, and will provide the series with ample amounts of Daylight Horror.
The benefits of the Purge will wear off over time.The purge's benefits, especially 1% unemployment, will be subject to diminishing returns, due to the heightened employment being a direct symptom of Purge-related damage. As people get better at preparing for the Purge, the need for extra jobs will decrease, due to the surge of employment being primarily in areas like medicine, construction, and security, added solely due to the injury and destruction caused by the last Purge. Eventually though, people will build better bridges, buildings, and become more personally prepared for the Purge, and the costs will start to outweigh the benefits.